The present invention relates to a novel optical digitizer for determining position of graphic data described on a recording medium such as a paper sheet. Particularly, the present invention relates to an optical digitizer configured so that a cursor is movable on a patterned member comprising fluorescent media to optically recognize the position information of the cursor from a projected image of the pattern, thus to determine position coordinates of graphic data on a recording medium.
Hitherto, a large number of position coordinates reading or recognizing devices called "digitizers" or "data tablets" have been commercialized. Such devices are operative to detect position coordinates at the time designated by a cursor slidable on a planar member. They find wide application in devices for inputting figures or characters into a computer. The above-mentioned position coordinates represent coordinate values designated by a lateral (X-axis) coordinate position and a longitudinal (Y-axis) coordinate position. For conventional digitizers, there have been proposed a system of utilizing electrostatic coupling or electromagnetic coupling, a system of utilizing voltage dividing ratio by resistors, a system of utilizing a magnetostriction phenomenon, and a system of utilizing ultrasonic wave etc. Among these systems, the digitizers of magnetostriction system have been widely utilized. They are configured so as to allow magnetostrictive pulses to be periodically propagated on a metal plate from the upper edge and the lefthand edge thereof to detect the propagation of the magnetostrictive pulses by means of a coil attached to a cursor, thereby calculating a propagation time of the magnetostrictive pulses to determine coordinates. Such a propagation time is determined based on a counted value of a counter circuit. Usually, the propagation speed of the magnetostrictive pulse is approximately 5000 m/sec. Accordingly, it is necessary to operate the counter circuit using a clock having about 100 MHz in order to obtain position coordinates with an accuracy of 0.1 mm.
However, the drawback with the above-mentioned digitizers of magnetostriction system are as follows. It is difficult to miniaturize a circuit for generating magnetostrictive pulses. Further, an excessive increase in an area of the planar member results in lowering of accuracy. Accordingly, the planar member must have a limited area. This makes it difficult to cover a wide data surface to be digitized. In addition, magnetostrictive pulses generate a large electromagnetic wave noise. In particular, when the digitizer is used in an office, the electromagnetic wave noise becomes a large noise source with respect to a private communication network, giving rise to communication fault.
To further consider problems with such a magnetostrictive digitization, a proposed digitizer shown in U.S. Pat. No. 3,904,821 will be briefly described. The coordinate digitizer comprises a data surface provided with a magnetostrictive sheet serving as nondirection transmission media, and vertical and horizontal wire conductors forming a field generating device positioned along the coordinate edges of the data surface. The coordinate digitizer further comprises trigger means for triggering the production of a magnetic field by the field generating device, and a pick-up device coupled to the transmission media and responding to the propagating vibrational mode for providing a signal to circuit means which will respond to the trigger means and to the pick up device in order to provide a position signal corresponding to the time of propagation of the vibrational mode from its time of generation to its time of pick-up.
The above-mentioned coordinate digitizer effects position determination by making use of propagation of a vibrational mode of longitudinal line strain wave across the entire axis of the nondirectional transmission media, thus providing improved operation and configuration as compared to previously proposed other digitizers operable based on the magnetostirictive principle. However, the aforesaid drawbacks generally encountered in conventional coordinate digitizers of this kind could not be solved by the digitizer disclosed in U.S. Pat. No. 3,904,821. Namely, the last-mentioned digitizer also required a pulse generator for triggering the field generating device, which is difficult to be small-sized. Also, there is a limit in regard to the size of the magnetostrictive sheet from a viewpoint of accuracy. Further, the employment of the magnetostrictive pulse results in occurrence of electromagnetic wave noise.